Polyester suture having improved knotting characteristics



United States Patent 3,390,681 POLYESTER SUTURE HAVING IMPROVED KNOTTINGCHARACTERISTICS Leonard D. Kurtz, Woodmere, N.Y., assiguor to SuturesInc., Coventry, Conn.

No Drawing. Continuation-impart of application Ser. No. 220,085, Aug.28, 1962. This application Apr. 4, 1966, Ser. N 0. 539,637

8 Claims. (Cl. 128335.5)

ABSTRACT OF THE DISCLOSURE A surgical suture having improved knottingcharacteristics. A multifilament thread of polyester fibers, preferablypolyethylene terephthalate, is combined with Teflon such that Teflondeposited in the interstices of the suture, reduces the tendency of theknot throw to open and Teflon deposited on the external surface of thesuture enhances the ability of the suture to snug down.

This is a continuation-in-part of my co-pending application Ser. No.220,085, filed Aug. 28, 1962.

This invention relates to surgical sutures. More particularly, theinvention relates to polyfilamentous non-absorbable surgical sutures ofimproved k'notting characteristics.

As used herein, the term suture includes surgical strands used to sewtissue as well as those used to tie off blood vessels and the like. Thusthe term includes strands sometimes referred to as ligatures.

Sutures are classified as either absorbable or nonabsorbable and may beeither polyfilamentous or monofilamentous. For the surgeon, thepolyfilament sutures, which may be braided, woven, twisted or spun, havesuperior knotting characteristics relative to a monofilament suture ofthe same material and it is to this type of suture that the presentinvention relates.

There are several polyfilament sutures of the nonabsorbable type inpresent use. Silk, for example, ha been used for years. There areseveral synthetic fibers which have been proposed for use as suturesand, among them, polyester fibers have characteristics which render themparticularly suitable for use as a surgical suturing material. Thesefibers are made from the linear condensation polymeric product producedby the reaction of a difunctional carboxylic acid and a diol. Chiefamong such polyester fibers are polyesters of the terephthalate typesuch as Dacron which is available as a suture. Dacron fibers are madefrom polyethylene terephthalate which is the reaction product ofethylene glycol and terephthalic acid. Polyesters from other diols anddicarboxylic acids may also be used such as, for example, polyestersfrom the reaction of ethylene glycol with both isophthalic andterephthalic acids. Other diols, such as cyclohexane dimethanol may alsobe used with the phthalic acids to produce fiber-forming polyesters fromwhich non-absorbable polyester sutures can be fabricated. Polymericlinear polyester materials of the foregoing type are illustrative of thelinear polyester fibers useful for making sutures which can be improvedaccording to the present invention. Terephthalate type polyester fiberssold under the trademarks Dacron, Kodel and Terylene are illustrativeand are more fully described, for example, in US. Patents 2,465,319 and2,901,446. Sutures fabricated from these fibers are made under rigorousconditions to ensure freedom from contaminants in amounts which wouldnot be tolerable for use as a suture.

Dacron and several other polyester fibers have a lower reaction withinthe tissue than silk and have a higher tensile strength. The material isnaturally water proof 3,390,681 Patented July 2, 1968 "ice and thereforeis non-capillary. All of these properties indicate that the polyesterfiber could be fabricated into an excellent non-absorbable suture, butthe knotting characteristics thereof are so poor relative to silk as toseriously prejudice the surgical use thereof. Knots in polyfilamentpolyester have a definite tendency to loosen considerably from the pointat which the knot was formed. Furthermore, the second throw tightens onthe first throw at its loosened point and does not snug down the firstthrow. Thus, no matter how many knots are used, the first throw is notsnugged down and the last knot has a tendency to open.

Polyfilament Dacron polyester sutures, despite the foregoingdisadvantages, are nevertheless used in certain situations and as manyas nine throws are employed to give acceptable knot security. Ingeneral, this amounts to at least one additional throw than is requiredwith silk, but the need for additional throws does not appear to be themain prejudice against the use of Dacron polyester sutures in surgery.The main prejudices seem to be the loosening of the first throw and theinability of a second throw to snug down the first throw when theloosening has occurred.

It is an object of the present invention to provide polyfilamentpolyester sutures of improved knotting characteristics.

These and other objects which will become apparent in light of thefollowing detailed description which includes a preferred embodiment,are achieved according to the invention by providing a polyfilamentpolyester suture, such as a Dacron suture, with polytetrafluoroethylenein the manner described.

According to the present invention, the knottability of polyfilamentpolyester sutures is considerably improved by providingpolytetrafluoroethylene on the surface and within the intersticesthereof. It has been found that by thus providing a polyfilamentpolyester, for example Dacron, suture, with Teflon, the tendency of thefirst knot throw to open is remarkably reduced. Furthermore, a secondknot throw is able to snug down the first knot throw and thus theinvention overcomes the main prejudice against the surgical use of anotherwise highly desirable suture. Still further, the improvement inknottability is not achieved at any sacrifice in other properties of thesuture. The coated suture is equally as inert as the uncoated suture.

EXAMPLE A 4-0 Dacron suture was passed through a suspension of Teflon inwater. The suture was of conventional size having a 4 thread core ofdenier 56 and a 12/2 thread cover having a denier of 336. Total denierwas thus 392. The Teflon suspension was obtained by diluting acommercially available blend (Du Pont 2510) which contains 58% Teflonparticles by weight in water. A tenfold dilution was employed. Theparticle-s are in the /2 micron size range and were suspended with theaid of a wetting agent (Triton X-100, Rohm and Haas). The suture sotreated was then washed to remove any excess material and then dried.The treated suture was found to have increased in weight by less thanone percent which represents the amount of Teflon incorporated on thesurface and within the interstices of the suture. The treated suture wasthen hot stretched to reduce the elastic memory thereof. This wasaccomplished by stretching the suture approximately 40% basedon itsoriginal length at a platen temperature of 450 F. on a hot stretchingmachine made by the W. M. Steele Company (Model As a control, anidentical Dacron suture, without being first impregnated with Teflon,was similarly stretched.

Knottability of the treated suture was compared with the untreatedsuture. by tying knots of each on a polished steel cylinder of aboutdiameter. The treated suture had noticeably less tendency to loosen.Both knots were then intentionally loosened to the same extent and asecond knot throw was then added to each and was observed to snug downthe knot of the treated suture but not of the untreated suture. Thesnugged down knots also tended to remain down and the second throw wasnot observed to loosen. A square knot was then provided in the treatedsuture well above the snugged down knot. A square knot similarly locatedon the untreated suture simply locked and the suture broke on beingpulled tight.

The treated suture was also noticeably more flaccid than the untreatedsuture. This property is graphically demonstrated by coiling an equallength of each suture into a one inch coil and comparing the propertiesof the coil. The untreated coil is markedly more springy.

Other Dacron polyester sutures ranging in sizes from to 6-0 weresimilarly treated and it was found that knotta'bility of the thread wasimproved with the addition of up to 2 weight percent and above of Teflonbased on the weight of the polyester. At higher levels the suture wassoft, but was quite slippery on the surface. Accordingly, it ispreferable to keep the amount of impregnation below 4% and even morepreferable to keep the impregnation below 1% so that the improvedknottability is not offset by a high degree of surface lubricity. Theamount of impregnation can be easily controlled within any desiredlimits by varying the concentration of Teflon or the length of time ofimpregnation or both.

The Teflon particles should preferably be small and several commerciallyavailable blends having average particle sizes below 1 to microns areavailable and suitable. The sutures can be simply immersed in the Teflonsuspension or continuously drawn therethrough. Suitable stabledispersions, described in Berry, U.S. Patent No. 2,478,229, can be used.It is preferred to dilute these dispersions to keep the amount ofimpregnation low.

The Teflon particles are tenaciously held by the sutures and will notseparate therefrom in an aqueous environment or under torture testingsuch as repeated washing or testing with high-velocity water streams.The impreghated suture has been found to be no more reactive thanuntreated sutures in thousands of clinical cases.

The improvement in knotta'bility of the sutures impregnated with Teflonaccording to the invention is remarkable. With levels of Teflon as lowas /2 A and even less by weight of Teflon, the improvement inknottability is noticeable and can be graphically demonstrated bycomparing the properties of coils of the treated material with similarlysized coils of untreated material. The knotting characteristics of thetreated suture approach those of the surgeons norm (waxed silk) and yetall the advantages of the synthetic over silk are retained.

The improved knotting characteristics achieved by the present inventionare perhaps explained by the following theoretical analysis of knotting.

One important factor in knotting is the relationship between the numberof throws and the security of the knot. If a loop formed by a knot issufficiently pulled, the knot will either open (disrupt) or break. Allother factors being equal, knot security, or tendency not to open, willbe in direct proportion to the number of throws until a point is reachedwhere additional throws are ineffective. After that point is reached,continued pulling will simply break the knot. The knot has reached itsmaximum security. Each surgeon is aware of this relationship and eachpasses his own judgment. In the caseof polyfilament polyester sutures,such as Dacron, surgeons use from three to nine throws for a completeknot de pending on circumstances.

Another factor is surface lubrication which is related to the nature ofthe lubricant and the amount and distribution thereof on the surface inquestion. It is apparent that a siliconized silk suture is more slipperthan a throw to bike waxed silk suture and that a Teflon coatedpolyester suture is more slippery than a wax coated polyester suture. Atthe same time, heavier coats of any given lubricant will give higherdegrees of lubrication than minimal coats thereof.

A further factor is the ability of the suture to tighten on itself. Oneof the striking characteristics of silk sutures is the ability of theknot to tighten on itself when the patient strains, coughs, sneezes orin any way pulls on the loop of the suture. If a waxed silk suture isknotted with three throws, well laid, squared, and snugged and the earsleft when the surgeon cuts his knot are 0.1 inch long, the majority ofthese knots will disrupt under increasing tension on the loop but theknot will not break. When exactly the same technique is used, and theears are 0.3 inch or longer, a great majority of these knots will breakand not disrupt. The only difference is the size of the ears. Thisproperty is undoubtedly the manifestation of the property of the throwsof the knot to lock against each other. It is considered that thisproperty is related to lubrication of surfaces. When an unwaxed silksuture is used, the three-throw technique with 0.1 inch ears go to theknot-break. In fact, two throws with 0.1 inch cars go :to theknot-break. The lack of lubricity on the surface permits locking of thethrows against each other with no displacement. In the same way,polyester suture knots will go to knot-break with three throws and a 0.1inch ear. When the surface is highly lubricated with Teflon, using thesame technique exactly, practically all the knots will disrupt. Inessence, the ability of a suture to snug itself is therefore related tothe lubricity of its surface.

Another factor is stiffness of the suture. All throws are affected bythis stiffness. The first knot throw tends to open, losing its line ofapposition because the suture is sharply flexed at the throw. The suturehas inherent energy which tends to straighten it. If this hiking upwarddoes occur, it is necessary for the next throw to restore the knot toits original position. But the second throw is also affected bystiffness. It tends to open for exactly the same reason the first throwtended to open. The same process continues right through the making ofthe entire knot, be it the first throw or the ninth. All have the sametendency to open when unrestrained. It should be obvious that thetendency to open would be in direct proportion to the degree ofstiffness, i.e., the greater the stiffness, the greater the tendency toopen. It has been observed that polyester sutures, which are markedlystiff, have an appreciable tendency to open in such surgical proceduresas suturing a heart valve. This surgical use involves continuousoscillation of the suture and as many as nine throws have been used inan attempt to delay or defeat the spontaneous opening of the sutureknot. Other factors such as elasticity and construction of braidobviously affect knotting but are not directly relevant to the presentinvention.

In impregnating the Dacron with Teflon, an unusual result was observed,which can be explained in retrospect. The braided suture apparentlybecame much softer than before the impregnation. It should be realizedthat the ability of the suture to change its contour without inherentstrain is dependent upon the ability of the internal portions of thatsuture to rearrange themselves in such a way that the strain isminimized or absent. With monofilaments, there cannot be anyrearrangement of the internal forces since all cross-sections are lockedto all other cross-sections. In polyfilarnentous materials, such asbraided Dacron, it should be possible for the multiple filaments whichmake up the suture strand to rearrange themselves to relieve the stress.Most likely, the addition of Teflon into the braid itself expedites thefibrils sliding over each other and therefore decreases the amount ofinternal stress when the contour of the suture is changed. With thedecrease in stiffness, the tendency of the first upward is decreased.The ability to lock all throws together is increased. The tendency ofthe last throw to open spontaneously is decreased. In essence, thetendency of the knot to open spontaneously, almost disappears. Thesurgeon has a much easier time making the knots.

Finally, the surface of Dacron has too high a coefiicient of friction.When the first throw hikes upward, with a square knot technique, thesecond throw locks into the first throw and is unable to restore thefirst throw to its original position. The surgeon has to start all overagain. When Teflon lubricates the surface of the polyester and the firstthrow does hike up, it is easy to push the first throw back to the lineof apposition with the second throw. With these two throws holding, itis easy for the surgeon to complete his knot. Finally, the relativesurface lubrication is highly important in the process of self-snugging.It is found that varying the concentration of Tefion on the surface ofpolyester braid will give control of this process. The most widely usedand satisfactory suture as far as knotting technique is concerned hasbeen surgical silk. By providing Teflon on a polyester suture inaccordance with the present invention, it is possible to closelysimulate the silk technique with the polyester suture, which is a markedadvance.

While the details of the invention have been described with reference toDacron type polyester, polyfilament sutures of other polyester fiberswhich have similarly poor knotting characteristics can be similarlyimproved by impregnating such sutures in accordance with the presentinvention. For example, sutures of Kodel and other linear polyesters ofthe terephthalic acid type can be used.

The sutures provided by the invention can be sterilized by themanufacturer or the user by known techniques, for example by autoclave,ethylene oxide or electromagnetic radiation. The sutures can also beprovided in sterile packages. The sutures may be provided in cut lengthsof for example, 18 inches to 36 inches or on spools. The sutures canalso be provided attached in known manner to surgical needles which maybe eyed or eyeless.

The Dacron polyester fiber from which the suture is fabricated may beany of several commercially available such as Du Pont type 5 5 which wasused to make the suture of Example I. Stretching of the suture isaccomplished by techniques known per se in the art in connection withpolyesters. The polyesters are conveniently stretched at platentemperatures up to just below temperatures at which the polyester sticksand the degree of stretch may be up to the breaking point andconveniently up to 50%. There is nothing unusual about this hotstretching step and techniques known to the applicable to polyesterfibers generally are applicable to the present polyester sutures toreduce or eliminate the elastic memory of the fibers of which the sutureis composed. However, the hot stretch- 3 ing step does reduce the sizeof the suture material and this is advantageous for surgical uses. TheTeflon dispersion is preferably of low concentration such as below 50%and preferably below 20% and lower to keep impregnation below thepreferred maximum.

What is claimed is:

1. A surgical suture of improved knotting characteristics consistingessentially of a multifilament polyester thread, said polyester being acondensation polymeric reaction product of a dicarboxylic acid and adiol, and polytetrafluoroethylene, said polytetrafluoroethylene beingdeposited in the interstices of the said thread to improve knottingcharacteristics of the suture by reducing the tendency of the knot notthrow to open.

2. A surgical suture of improved knotting characteristics consistingessentially of a multifilament polyethylene terephthalate thread andpolytetrafluoroethylene, said polytetrafluoroethylene being deposited inthe interstices of the said thread to improve knotting characteristicsof the suture by reducing the tendency of the knot throw to open.

3. A surgical suture of improved knotting characteristics consistingessentially of a multifilament polyester thread, said polyester being acondensation polymeric reaction product of a dicarboxylic acid and adiol, and polytetrafluoroethylene, said polytetrafluoroethylene beingdeposited on the external surface of the thread to improve the knottingcharacteristics of the suture by enhancing the ability of the suture tosnug down.

4. A surgical suture of improved knotting characteristics consistingessentially of a multifilament polyethylene terephthalate thread andpolytetrafluoroethylene, said polytetrafluoroethylene being deposited onthe external surface of the thread to improve the knottingcharacteristics of the suture by enhancing the ability of the suture tosnug down.

5. A surgical suture as claimed in claim 4 wherein the said depositionof polytetrafluoroethylene on the external surface of the thread isintermittent.

6. A surgical suture of improved knotting characteristics consistingessentially of a multifilament polyester thread, said polyester being acondensation polymeric reaction product of a dicarboxylic acid and adiol, and polytetrafluoroethylene, said polytetrafluoroethylene beingdeposited in the interstices of the thread and on the external surfaceof the thread to improve the knotting characteristics of the suture byreducing the tendency of the knot throw to open and by enhancing theability of the suture to snug down.

7. A surgical suture of improved knotting characteristics consistingessentially of a multifilament polyethylene terephthalate thread andpolytetrafluoroethylene, said polytetrafluoroethylene being deposited inthe interstices of the thread and on the external surface of the threadto improve the knotting characteristics of the suture by reducing thetendency of the knot throw to open and by enhancing the ability of thesuture to snug down.

8. A surgical suture as claimed in claim 7 wherein the said depositionof polytetrafluoroethylene on the external surface of the thread isintermittent.

References Cited UNITED STATES PATENTS 2,193,188 3/1940 Bradley 128335.52,870,045 1/1959 Corkum 117-138.8 2,909,177 10/1959 Dowd et al. 128335.53,187,752 6/1965 Glick 128-3355 3,307,971 3/1967 Kurtz 117138.83,322,125 5/1967 Kurtz 128-3355 OTHER REFERENCES Postlethwait et al.:Wound Healing, Surgery, Gyne., & Obstet. May 1959, pp. 555-566.

Postlethwait et al.: Experimental Study of Polyester Fiber Suture, Amer.Jour. of Surg., vol. 102, November 1961, pp. 706-709.

DALTON L. TRULUCK, Primary Examiner.

Disclaimer and Dedication 3,390,681.Le0nard D. Kurtz, Woodmere, N.Y.POLYESTER SUTURE HAVING IMPROVED KNOTTING CHARACTERISTICS. Patent datedJuly 2, 1968. Disclaimer and dedication filed Apr. 22, 1968, by theassignee, Sutures 11w. Hereby disclaims and dedicates to the Public theterminal portion of the term of the patent subsequent to May 13, 1984.

[Oflicial Gazette October 8, 1968.]

